


High Risk, High Reward

by RatRacer



Category: Gravity Falls
Genre: Creampie, Established Relationship, F/M, Plot What Plot/Porn Without Plot, Semi-Public Sex, Sibling Incest
Language: English
Status: Completed
Published: 2018-12-07
Updated: 2018-12-07
Packaged: 2019-09-13 07:15:11
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 1,393
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16888032
Author URL: https://archiveofourown.org/users/RatRacer/pseuds/RatRacer
Summary: PWP - Dipper and Mabel have sex in a janitor's closet.





	High Risk, High Reward

If Mabel had to pick which feeling she hated the most, it would be boredom. She was a girl of action, always wanting to be busy doing something. Sadness, pain, fear, those were all things you felt because of something that happened. But boredom, that was what you felt when you were doing nothing. And for Mabel, waiting in front of a door definitely counted as nothing.

 

“Uuuuuugh, how long do we have to wait here? It feels like forever!” she said out loud.

 

“It’s been five minutes, not forever.” her brother answered while looking down on his phone. “And the janitor has always showed up within ten minutes so it shouldn’t be much longer.”

 

Mabel leaned back against the wall and sighed. Spending another five minutes just staring at a door would be like torture for her, so instead she closed her eyes and hoped some daydreaming would help pass the time. As her mind began drifting, she thought back to the day that this whole business had started…

 

_ It was just a few days before their last year in middle school was over, after the final exams and around that time that both the students and the teachers had given up trying to work. Knowing that their history teacher would just put on a movie and leave the classroom for an hour, Mabel had jokingly asked Dipper if he wanted to fool around in the back of the classroom, certain that he’d never take that kind of risk. But a few minutes into the film, she glanced over to see him pretend to pick something up under his desk, go down under it, and quietly crawl under her desk. Her heart began racing as he pushed her legs apart and put his head between her thighs... _

 

Her fantasy was interrupted by a nudge from Dipper. Coming back to reality, she saw the janitor going into the closet. She took her phone from her pocket and pretended to focus on it until she heard the door close and footsteps walking away. Both twins scanned the corridor to make sure nobody could see them, and quickly went into the closet.

 

Going in after his sister, Dipper immediately turned around and grabbed the door handle. Double-checking the hallway, he closed the door and went to lock it. But before he could, a noise from the back of the room got his attention. Looking back, he saw Mabel with her back up against the wall, lifting her skirt and pushing her panties to the side to give her brother a full view of her vagina. “I’m ready to go, bro-bro.” she said as soon as Dipper faced her. “Don’t keep me waiting~”

 

“But the door’s not-”

 

“If you lock it, there’s no risk that we’re caught. Didn’t you say you were into doing risky things in public?”

 

Dipper felt his pants tightening at Mabel’s words. Just having sex at school was exciting, but the thought that someone could open the door, look inside, see him  _ fucking his sister...  _

Leaving the door unlocked, he walked closer to Mabel and undid his fly, then pulled his penis out of his underwear. Stroking it with his left hand, he put his right hand to her vagina and rubbed her, feeling how wet she was already. He continued rubbing and fingering her for a couple of seconds until he was completely erect.

 

“Wait, before you start, I just need to ask you something.” Mabel said to him. She let go of her clothes and put her arms around Dipper, leaning in to whisper in his ear. “How does it feel, knowing you’re about to fuck your sister in a high school janitor’s closet?”

 

“It’s... It’s really scary.” Dipper answered. “Anybody could walk in on us, and they’d find out about our relationship, and fuck, I don’t even have a condom.”

 

Mabel moved a hand up to his head and stroked his hair. “And do you still want to do it?” she asked. Dipper nodded in response. “Even if somebody could see us?” Another nod. “Even if you might not pull out in time?” A moment passed before he nodded for the third time. “That’s what I like to see. Now put it inside me, Dipper.”

 

Doing as he was told, Dipper moved his hips closer to Mabel, putting his tip right up to her lips. Putting a hand on her hip, he used the other to align himself as he pushed forward to finally penetrate her. As soon as his head slipped inside Dipper couldn’t help but to let out a moan, which was quickly followed by Mabel doing the same. They had always used condoms before, so the feeling as he slipped his penis deeper inside her pussy was completely new to them both.

 

“Oh Mabel, you’re so warm and- and so wet...” Dipper moaned as he went further, getting the full length of his dick into Mabel. Once he felt himself bottoming out, he put his other hand on her hips and began thrusting, going for the long slow thrusts his sister loved. “Am- am I doing it right?”

 

“Yeah, you’re doing it so right...” Mabel answered. “Just, could you rub my clit a bit too?” When she felt one of Dipper’s hands move in between them and start lightly stroking her button, she tightened her hold around him. “Yes, that’s perfect! Just keep doing that, please!” she told her brother before shoving his head closer to hers and locking lips with him. Just as Mabel wanted, Dipper kept rubbing her clit as he almost pulled out completely, then slowly thrust in as deep as he could.

 

With his hips, hand, and mouth occupied Dipper found it almost impossible to think about anything other than the pleasure he felt as Mabel’s pussy squeezed around him. Accepting his fate, he let himself get lost in the moment as he sloppily made out with his sister, continuing to thrust, and thrust, and thrust... He was finally brought back to reality when he felt his dick twitching, realizing he was getting dangerously close. Stopping his hips, he pushed his head out of Mabel’s tight grip so he could talk. “W-wait!”

 

“What’s wrong?” asked Mabel? “Did you hear something?”

 

“No, but I’m getting pretty close to cumming, I-” Dipper began, until he felt her tighten around him. “I know I should pull out, but it feels so good! Can I...”

 

“Can I what?” Mabel responded. “You gotta tell me what you want, bro.”

 

Dipper moved his hands away and wrapped them around her before speaking up. “Can I cum inside, Mabel?”

 

Instead of words, Mabel answered by pushing her brother back into their kiss and putting one of her legs around both of his. Locked in place Dipper started moving again, hilting himself inside her and fucking her in short, quick thrusts. Both of them got louder and louder, not caring if their muffled moans could be heard through the door, only focusing on Mabel’s dripping cunt around Dipper’s twitching cock, going faster and faster until...

 

Dipper nearly screamed into his sister’s mouth as he finally came, shooting out jet after jet of semen as deep as possible inside of her. Mabel joined in with a cry of her own once she felt her brother filling her in a way she had never experienced before. Joined together, almost half a minute passed until Dipper’s penis started to shrink and he pulled out. Instantly, Mabel put a hand over her vagina to prevent any cum stains. Breaking the kiss, they both stared into each others eyes as the realization of their actions slowly hit them.

 

“That was, uh...” Dipper started. “I mean, it felt great! But, you know.”

 

“Yeah, I should’ve told you to finish in my mouth instead.” Mabel answered. “Sooo, I should probably go see if I can get some morning-after pills after school. And try to stop myself from leaking your jizz all over.”

 

“Well, I could help you with the second thing. I’ve always wondered what it’s like to lick someone afterwards.” Dipper sheepishly admitted.

 

Mabel thought for a moment before nodding. “Fine, but only if you come with me to the pharmacy later, for moral support.”

 

“Deal.” Dipper replied as he went down on his knees, pushed her legs apart and put his head between her thighs...


End file.
